This project will examine the temporal patterning of autonomic, central nervous system and somatic activity during sleep-waking states in normal infants and infants at risk for the Sudden Infant Death Syndrome (SIDS). The objective is to determine whether sleep disturbances, previously noted in infants at risk for SIDS, results from a failure to arouse from apneic and other transient events during sleep. Physiological activity during sleep will be examined by measuring EEG, somatic activity, and cardiac rate variability before and after apnea and transient events of sleep, and during transition periods between states. These studies will be carried out on data already collected from normal infants and siblings of SIDS victims over the first 6 months of life. The integration of sleep states will be studied by examination of coupling between sequencing of particular states and temporal patterning of physiological activity. The presence of fast ultradian periodicities will be studied in each age group.